"You could add something about that (i.e. not possible to draw a team from country X if you have already one in you group, excepted if there is already on in each group)"

I disagree.
I so no reason why a team from a specific Nation couldnt be in the same group with other teams of same nation. I dont agree that there should be restrictions how those teams are divided into grouops.

Exameple CL Football, you do have conditions like those and see what happens, 95% of teams that are qualified into 1/4s or semis are England, Spanish, Italian, German.

So in my opinion this "rule" will only make stronger nations stronger and weaker nations weaker...

Bad comparison I think, because in football you can buy players from other countries, and money is the only basis. In NC the only basis is country, and ther's less fun to play teams from your own country